Problem with Map Key Validation

[bbuske (Benjamín Buske)]

Hi,

I am fairly new to go and just work on my first project, which has gotten along quite well so far. However, I have a strange problem now with validation of map keys. I am trying to create a simple flash card app, that asks for a card and then for a definition. If either the card or the definition exist already, it should throw an error and let the user enter the term again. This is my code (I have cut unnecessary cases out):

package main

import (
	"bufio"
	"fmt"
	"os"
)

func main() {

	fmt.Println("Flash Cards v. 1.0")

	var choice string
	var card string
	var definition string
	cards := make(map[string]string)

	for {
		fmt.Println("Input the desired action (add, remove, import, export, ask, exit):")
		fmt.Scan(&choice)

		switch choice {
		case "add":
			scanner := bufio.NewScanner(os.Stdin)
			scanner.Scan()
			for {
				fmt.Println("The card: ")
				scanner.Scan()
				card = scanner.Text()
				if _, ok := cards[card]; ok {
					fmt.Printf("The card %s already exists. Try again:\n", card)
					scanner.Scan()
					card = scanner.Text()
				}
				fmt.Println("The definition for the card:")
				scanner := bufio.NewScanner(os.Stdin)
				scanner.Scan()
				definition = scanner.Text()
				if _, ok := cards[definition]; ok {
					fmt.Printf("The definition %s already exists. Try again:\n", definition)
					scanner.Scan()
					definition = scanner.Text()
				}
				cards[card] = definition
				fmt.Printf("The pair %q:%q has been added\n", card, definition)
				break
			}
		case "remove":
		case "import":
		case "export":
		case "ask":
		case "exit":
		default:
			fmt.Println("Error. Please try again!")
		}
	}
}

The program runs fine. I enter add. It asks to enter a card, so for example, I enter France. Then it asks for a definition, and I enter Paris. I get the message The pair France:Paris has been added and get back to the menu, enter add again, and it asks for a card. If I now enter France again, I get the error saying The card France already exists. Try again. so if I now enter Germany it does accept the entry and asks for a term/definition. But if I now enter Paris again, it says The pair Spain:Paris has been added.

Instead, it should be giving a warning, saying that the definition Paris already exists and then ask the user to enter a new term, as it does above with Paris. I have been looking at the code and at various sources and docs, but I couldn’t figure it out. I am sure it is some minor issue, I am not considering.

Any help would be appreciated.
Cheers,

Ben

[NobbZ (Norbert Melzer)]

You are checking if the definitioni already exists as a key in the map, but store it only as a value. This will never succeed.

You either need to iterate over all values in the map for k, v := range cards { … } or alternatively keep a “reverse lookup map”, which maps a definition to its card.

The latter requires more memory, while the former has a longer runtime with each item you add to the map.

[bbuske (Benjamín Buske)]

Hi,

thanks for your reply.

I haven’t thought about that.

Since I have not yet been dealing with reverse lookup, but only with iterating over a map, I will go with that solution for now. Data should be low and contain up to 5 or 10 key pairs. It is also just a challenge for the course. While it likely will serve as some reference or base of code in the future, it is unlikely to be used for anything else later on, let alone in a production environment.

Cheers